1. Field of the Invention
The present invention relates to a transformer and more particularly to a support assembly for holding transformer components in precise operative relation.
2. Description of Related Art
In designing a transformer several factors must be considered. First, to obtain desired electrical and magnetic performance characteristics, a transformer must have precise and stable predetermined spacial relationships between the coils and cores of the transformer. While these relationships will vary among transformers depending on the characteristics desired, the transformer support assembly must hold the components in the desired relationship to ensure constant performance characteristics during use.
While precise and stable relationships between transformer components may be ensured by use of complex and rigid supporting structure, such a structure will increase the costs of material and manufacture. Thus, for economical manufacture of transformers, the support assembly must be designed to minimize material costs, to provide for simple assembly-line production and to allow for certain manufacturing tolerances while ensuring precise and stable relation between components during operation.
Another factor in designing transformers concerns the distance between conductors of opposite polarity. There must be a minimum separation between the primary and secondary coils to ensure proper operation of the transformer. This separation, commonly defined in terms of creepage and clearance distances, will depend on whether the coils are potted in a compound. In compound-filled coils, the potting compound significantly increases the cost of the transformer and may also limit heat dissipation.
To avoid the disadvantages of compound-filled transformer coils, unpotted transformers have been used. These transformers require larger creep paths and clearance for insulation between coils and between coils and associated magnetic cores. Where small transformers are designed, creepage and clearance becomes critical.
The transformer disclosed in British Pat. No. 1,339,151 to Hinchley Engineering Co. is taught to provide sufficient creepage and clearance between the components. Primary and secondary coils are wound on bobbins which are mated to opposite sides of a separator and the legs of opposed U-shaped cores are disposed in bores in the bobbins. Since the coils are potted, the structure of the transformer does not provide creepage and clearance distances required for air cooled transformers. Additionally, the structure does not provide means for securing the cores in precise, stable relationship to each other and to the coils.
A ferrite choke coil is taught in British Specification No. 146,847 filed by American Telephone & Telegraph Co. This device incorporates a single E-shaped core the center leg of which is disposed in the post of support assembly around which are wound primary and secondary coils axially separated by a wall. The core is rigidly held in position by locking tabs on jaws engaging its base; such a rigid structure does not allow for certain manufacturing tolerances thereby increasing material costs. The extremely close relationship between the coils and between the coils and the core legs suggests a lack of concern for creepage and clearance which must be considered in small, air-cooled transformers.
The present invention overcomes the disadvantages of prior art transformer support assemblies by providing a support structure which is easily assembled, which ensures precise and stable component relationships with adequate creepage and clearance for use of air- cooled coils, and which allows for certain tolerance build-up in the components.